Question

comprehension check!

1. what are the three subatomic particles that make up an atom?
2. where are protons and neutrons located in an atom, and what is their charge?
3. how does the mass of an electron compare to the mass of a proton or neutron?
4. how can you determine the number of neutrons in an atom using isotope notation?
5. what is the difference between the atomic number and the mass number of an element?

Explanation:

1. Protons (positive charge), neutrons (no charge) are in the nucleus. Electrons (negative charge) are in electron - shells around the nucleus.
2. The mass of an electron ($\sim9.1\times10^{-31}\text{ kg}$) is much smaller than that of a proton ($\sim1.67\times10^{-27}\text{ kg}$) or neutron ($\sim1.67\times10^{-27}\text{ kg}$).
3. In isotope notation $\ce{^A_ZX}$, $A$ (mass number) = number of protons ($Z$) + number of neutrons. So, number of neutrons = $A - Z$.
4. Atomic number ($Z$) is the number of protons. Mass number ($A$) is the sum of protons and neutrons.

Answer:

1. Protons (positive), neutrons (neutral) in nucleus; electrons (negative) in electron - shells.
2. Electron mass $\ll$ proton/neutron mass.
3. Number of neutrons = mass number - atomic number (from isotope notation $\ce{^A_ZX}$: neutrons = $A - Z$).
4. Atomic number: number of protons. Mass number: sum of protons and neutrons.
5. Atomic number = number of protons. Mass number = protons + neutrons. Difference: mass number - atomic number = number of neutrons.